It is desirable to measure as accurately as possible and display to an operator of a vehicle the amount of liquid fuel in the vehicle fuel tank. The most commonly used method of measuring the amount of fuel in a tank includes a float connected to an arm which in turn is connected to a wiper for wiping along a pattern of contacts on a resistor card. As the level of fuel in the tank changes, the float and arm move with the fuel level and the wiper moves along the surface of the resistor card changing the resistance in a circuit connected to a fuel gauge.
Such fuel level sensors are mounted within the fuel tank and it is difficult and expensive to replace the fuel level sensor within a tank in the event of failure of the sensor. It is therefore desirable to provide a fuel level sensor that will not fail during the useful life of the vehicle. On the other hand, improvements in automobile technology have resulted in vehicles having a longer useful life. Shortages of fuel oil have resulted in searches for alternatives to fossil fuel and in particular to the development of methanol, which is known to be particularly corrosive. Furthermore, it is becoming increasingly evident that vehicle emissions contribute adversely to the environment and environmental concerns, and environmental legislation, have led to the formulation of complex additives to liquid fuel to reduce certain emissions, but these additives also adversely effect the compounds from which the resisting elements of the resistor cards are made. It is desirable, therefore, to have a level sensing device that is sealed against contact from the liquid fuel but can provide an electronic signal indicative of the level of fuel within a tank.
In my recent patent application Ser. No. 10/883,155 filed Jul. 1, 2004, I disclosed a fuel level sensor employing two magnets with like poles directed toward each other and a magnetic strength detector that is moveable toward one magnet and away from the other in response to changes in the level of fuel in the tank. Such a detector will provide an output that is linearly related to the level of fuel in the tank, however, fuel tanks are often irregular in shape and therefore a detector having an output that can be nonlinearly related to changes of the fuel level, such as can be provided by a resistor card, is desirable.
Efforts have been made to seal a resistor card within an enclosure and include within the enclosure a moveable, magnetic contact element that is responsive to a magnetic field originating from a moveable magnet outside the enclosure. The magnet is connected to the end of a wiper which in turn is connected to a float arm such that changes in the fuel level will cause the magnet to move along the surface of the enclosure causing the moveable contact within to move responsive to changes in the fuel level within the tank.
There are such circumstances, however, when such magnetic detectors are not useable. It would be desirable, therefore, to provide a fuel level detector that responds to changes in the level of fuel in a tank but is itself sealed within an enclosure so as to prevent contact with the fuel into the interior of the detector.